The present application relates to a wobble signal extraction circuit and an optical disk device including the same.
In general, in a recording optical disk, in order to indicate disk positional information or the like, a wobble signal called a wobble is previously recorded in a groove becoming a track. For example, in the case of a CD-R/RW, a frequency of 22.05 kHz which is sufficiently lower than 4.3218 MHz as a frequency of a basic clocking signal for an RF (Radio Frequency) signal desired to be recorded is used as a basic frequency of the wobble signal. In addition, in the case of a DVD+RW, a frequency of 818 kHz near 26.16 MHz as a frequency of a basic clocking signal for an RF signal is used as a frequency within a frequency band of the wobble signal.
A method of arithmetically operating a push-pull signal component {(A+D)−(B+C)} for signals (A, B, C, D) from light receiving portions which is obtained by dividing a photo detector (PD) in quarters is known as a method of detecting the wobble signal recorded in the optical disk device. In this case, the wobble signal detected is converted into address information by using an address decoder, thereby making it possible to obtain positional information for recording and reproducing. Here, a noise component is hardly contained in an unrecorded portion in which no RF signal is recorded. Therefore, even when there is a gain difference between channels for signals (A+D) and (B+C), this gain difference merely becomes an offset, and thus there is caused no problem in detection of the wobble signal.
In a recorded portion in which the RF signal is already recorded, however, when the gain difference is generated between the channels for the signals (A+D) and (B+C), leakage of the RF signal occurs in a phase of detection of the wobble signal. As a result, there is encountered a problem that the characteristics of the wobble signal is deteriorated.
In order to cope with this situation, Japanese Patent Laid-open No. 2005-353195 discloses a circuit configuration including two variable gain amplifiers, two detectors, a comparator, and a gain controlling section. In this case, the two variable gain amplifiers change output signals (A+D) and (B+C) from a light receiving element divided into halves at arbitrary gains, respectively. The two detectors detect output signals from the two variable gain amplifiers, respectively. The comparator compares output signals from the two detectors with each other. Also, the gain controlling section controls gains of the two variable gain amplifiers based on a comparison output from the comparator. Thus, the circuit configuration forms an Auto Gain Control (AGC) circuit for causing gain balances between the channels for the signals from which a push-pull signal is obtained to agree with each other.